This invention relates to circuitry for reducing the energy consumption of fluorescent lamps and more particularly to new and improved circuitry for reducing the energy consumption of a rapid-start two lamp fluorescent lighting system of the type which utilizes a sealed ballast unit.
The rapidly increasing cost of energy has stimulated an effort to reduce the energy consumption of lighting systems used in homes, office buildings, retail stores and the like. Furthermore, some electrical utilities have been requiring certain customers to either reduce electrical power consumption or be financially penalized.
One widely used type of lighting system is a rapid-start fluorescent lamp fixture wherein two elongated fluorescent lamps are connected in series and coupled to the output of a sealed ballast unit. The ballast unit provides appropriate voltages and currents to start and operate the series-connected fluorescent lamps. The design of the system is such as to provide full lamp brightness. Because the ballast unit is sealed, modification of already existing lighting systems for energy reduction is impractical. Furthermore, large numbers of two lamp fixtures are commonly wired to one ON-OFF switch. Thus, selective turning off of fluorescent lamps is impossible unles the system is rewired.
Various approaches have been taken to save energy in rapid-start fluorescent lighting systems. Alternate pairs of lamps can be removed from the lighting system. However, uneven illumination is provided and significant reactive current is drawn by the unloaded ballast unit. U.S. Pat. No. 3,956,665, issued May 11, 1976 to Westphal, discloses another method of reducing energy consumption. One of the two lamps in the two lamp rapid-start system is replaced with a so-called phantom tube. The phantom tube consists of a capacitor sealed within a glass or plastic tube and connected between opposite ends thereof. When the phantom tube replaces a lamp in a two lamp rapid-start system, it preserves the series circuit thus allowing the remaining lamp to light. One disadvantage is that the use of the phantom tube results in an uneven light distribution since the tube produces no light of its own.
A capacitor coupled in series with the two fluorescent lamps of the rapid-start system has been utilized to reduce energy consumption by increasing the capacitive reactance of the load on the ballast unit. U.S. Pat. No. 3,954,316, issued May 4, 1976 to Luchetta, discloses a circuit comprising a capacitor and an isolation transformer for reducing energy consumption in a fluorescent lamp system. However, the isolation transformer is a relatively large, heavy, and expensive component. When the transformer is packaged at one end of a fluorescent lamp in a housing with the impedance-modifying capacitor, an appreciable portion of the useful lamp length is lost, and the lamp is heavier at the transformer end. Also, the cost of the isolation transformer and its associated housing is relatively high. U.S. Pat. No. 4,146,820, issued Mar. 27, 1979 to Bessone et al, discloses a power reducer for a rapid-start fluorescent lamp wherein a relay switches a current reducing capacitor in series with the lamp after a predetermined time interval.